In general, there are two settings that could be the reason for your sig not to be displayed. The first one is in your admin panel, where you can allow or deny the use of signatures on a global level. Go to "Users & Groups / Users / User Options" and set "Allow Signatures" to YES.

The second option can be found in your personal profile settings. Go to "Profile >> Preferences" and enable the option "Always attach my signature". Your signature should now be attached to all posts you make, if you actually have content in it.

Note: On some forum versions, it's possible that you still won't see your signatures on posts you have already made, although you have activated all necessary options. There is no other way to change this than to edit those posts and mark the box "attach my signature to this post" and save.